Recommended config ?

I found that at the moment, choosing the values for the config is fairly hard. It requires to spend a good amount of time reading the code to see what backend do with what, understand the default values, understand in what situation which backend is available ...

It would be very helpful I think if you could:
- provide a recommended configuration in the Readme
- say in `Config`'s doc what backend use the value and what the default is
- maybe have a table in the Readme that say which backend are active depending on the system ?